The goal of this paper -set in the context of the reform to lower the school starting age in Poland -is to investigate the determinants of parental decisions to enrol their six-year-old children in the 1 st grade versus leaving them in preschool or preparatory class. It was found that starting school before the compulsory term occurs primarily in response to objective symptoms of a child's readiness for school, but there is also some evidence for a deliberate investment in education by parents with a higher socio-economic status. Finally, early enrolment may also be driven by a cost-reducing strategy. The discussion highlights the possible reasons for the political failure of school age reform, which was recently cancelled after having been gradually introduced for six years.